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Networks & Protocols INF566 - X2010 - 2012 Lecture 3 - Enterprise Grade Routing - OSPF thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 1 Intro, kick-off, objectives and motivation (Thomas)

  1. Some Taxonomy thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  2. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 Router IDs selected independent of interface addresses 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  3. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 Router IDs selected independent of interface addresses Links 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  4. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 Address 10.1.5/24 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  5. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 4 2 1 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” 5 10.1.5/24 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  6. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 4 2 1 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” Metric in range [0 , 2 16 ] 5 (Metric can be asymmetric) 10.1.5/24 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  7. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of .1 .2 .4 .6 interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” .3 .5 Metric in range [0 , 2 16 ] 5 (Metric can be asymmetric) .3 .3 .5 .5 10.1.5/24 Interfaces 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  8. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of .1 .2 .4 .6 interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” .3 .5 Metric in range [0 , 2 16 ] 5 (Metric can be asymmetric) .3 .3 .5 .5 10.1.5/24 Interfaces 10.10.10.3 10.10.10.5 Address thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  9. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of .1 .2 .4 .6 interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” .3 .5 Metric in range [0 , 2 16 ] 5 (Metric can be asymmetric) .3 .3 .5 .5 10.1.5/24 Interfaces 10.10.10.3 10.10.10.5 Address From the “link prefix” thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  10. Some Taxonomy 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 Router IDs selected 10.1.1/24 10.1.4/24 10.1.7/24 independent of .1 .2 .4 .6 interface addresses 10.1.2/24 10.1.8/24 Links 10.1.3/24 10.1.6/24 3 2 3 1 Address Cost - called “Metric” .3 .5 Metric in range [0 , 2 16 ] 5 (Metric can be asymmetric) .3 .3 .5 .5 10.1.5/24 Interfaces 10.10.10.3 10.10.10.5 Address From the “link prefix” In this case, all .X are the same thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 10

  11. Link State Advertisements 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 10.1.1/24 10.1.4/24 10.1.7/24 .1 .2 .4 .6 10.1.2/24 10.1.8/24 10.1.3/24 10.1.6/24 3 2 3 1 .3 .5 5 .3 .3 .5 .5 10.1.5/24 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 11

  12. Link State Advertisements 10.10.10.1 10.10.10.2 .1 4 .2 2 .2 10.1.1/24 10.1.4/ .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 12

  13. Link State Advertisements 10.10.10.1 10.10.10.2 .1 4 .2 2 .2 10.1.1/24 10.1.4/ .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  14. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 10.1.1/24 10.1.4/ .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  15. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  16. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ Advertising Router: 10.10.10.1 = Router ID .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  17. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ Advertising Router: 10.10.10.1 = Router ID .1 .2 Number of links: 3 = 2 links plus router itself 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  18. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ Advertising Router: 10.10.10.1 = Router ID .1 .2 Number of links: 3 = 2 links plus router itself 10.1.2/24 10.1.3/24 Description of Link 1: Link ID = 10.1.1.1, Metric = 4 3 2 Description of Link 2: Link ID = 10.1.2.1, Metric = 3 .3 Description of Link 3: Link ID = 10.10.10.1, Metric = 0 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  19. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ Advertising Router: 10.10.10.1 = Router ID .1 .2 Number of links: 3 = 2 links plus router itself 10.1.2/24 10.1.3/24 Description of Link 1: Link ID = 10.1.1.1, Metric = 4 3 2 Description of Link 2: Link ID = 10.1.2.1, Metric = 3 .3 Description of Link 3: Link ID = 10.10.10.1, Metric = 0 5 .3 .3 Other stuff: 10.1.5/ checksum, sequence number, .... 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  20. Link State Advertisements 10.10.10.1 10.10.10.2 • LSA of router 10.10.10.1: .1 4 .2 2 .2 Link State ID : 10.10.10.1 = Router ID 10.1.1/24 10.1.4/ Advertising Router: 10.10.10.1 = Router ID .1 .2 Number of links: 3 = 2 links plus router itself 10.1.2/24 10.1.3/24 Description of Link 1: Link ID = 10.1.1.1, Metric = 4 3 2 Description of Link 2: Link ID = 10.1.2.1, Metric = 3 .3 Description of Link 3: Link ID = 10.10.10.1, Metric = 0 5 .3 .3 Other stuff: 10.1.5/ checksum, sequence number, .... 10.10.10.3 Each router sends its LSA to all routers in the network (using a method called reliable flooding) thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 13

  21. LSDB 10.10.10.1 10.10.10.2 .1 4 .2 2 .2 10.1.1/24 10.1.4/ .1 .2 10.1.2/24 10.1.3/24 3 2 .3 5 .3 .3 10.1.5/ 10.10.10.3 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 14

  22. 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 .1 4 .2 2 1 .2 .4 .4 .6 LSDB 10.1.1/24 10.1.4/24 10.1.7/24 .1 .2 .4 .6 10.1.2/24 10.1.8/24 10.1.3/24 10.1.6/24 3 2 3 1 Each router has a .3 .5 database which 5 .3 .3 .5 .5 contains the LSAs from all other routers 10.1.5/24 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 15

  23. LSDB • The collection of all LSAs is called the link-state database • Each router has and identical link-state database • Useful for debugging: complete network description • When neighboring routers discover each other for the first time, they will exchange their link-state databases • The link-state databases are synchronized using reliable flooding thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 16

  24. OSPF Packet Format OSPF packets are not carried as UDP payload! OSPF has its own IP protocol number: 89 TTL: set to 1 (in most cases) Destination IP: neighbor’s IP address or 224.0.0.5 (ALLSPFRouters) or 224.0.0.6 (AllDRouters) thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 17

  25. OSPF Header Format thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  26. OSPF Header Format 2: current version is OSPF V2 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  27. OSPF Header Format 2: current version is OSPF V2 Message types: 1: Hello (tests reachability) 2: Database description 3: Link Status request 4: Link state update 5: Link state acknowledgement thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  28. OSPF Header Format 2: current version is OSPF V2 ID of the Area Message types: from which the 1: Hello (tests reachability) packet originated 2: Database description 3: Link Status request 4: Link state update 5: Link state acknowledgement thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  29. OSPF Header Format 2: current version is OSPF V2 ID of the Area Message types: from which the 1: Hello (tests reachability) packet originated 2: Database description 3: Link Status request 4: Link state update 5: Link state acknowledgement Standard IP checksum taken over entire packet thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  30. OSPF Header Format 2: current version is OSPF V2 ID of the Area Message types: from which the 1: Hello (tests reachability) packet originated 2: Database description 3: Link Status request 4: Link state update 0: no authentication 5: Link state acknowledgement 1: Cleartext password 2: MD5 checksum Standard IP checksum taken (added to end over entire packet packet) thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  31. OSPF Header Format 2: current version is OSPF V2 ID of the Area Message types: from which the 1: Hello (tests reachability) packet originated 2: Database description 3: Link Status request 4: Link state update 0: no authentication 5: Link state acknowledgement 1: Cleartext password 2: MD5 checksum Standard IP checksum taken (added to end over entire packet packet) Authentication passwd = 1: 64 cleartext password Authentication passwd = 2: 0x0000 (16 bits) Prevents replay KeyID (8 bits) attacks Length of MD5 checksum (8 bits) Nondecreasing sequence number (32 bits) thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 18

  32. OSPF LSA Format LSA Header Link 1 Link 2 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 19

  33. Know Thy Neighbors thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 20

  34. Know Thy Neighbors • Routers multicasts OSPF Hello packets on all OSPF- enabled interfaces. thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 20

  35. Know Thy Neighbors • Routers multicasts OSPF Hello packets on all OSPF- enabled interfaces. • If two routers share a link, they can become neighbors, and establish an adjacency OSPF HELLO 10.10.10.1 10.10.10.2 Scenario: OSPF HELLO: I heard 10.10.10.2 Router 10.1.10.2 restarts thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 20

  36. Know Thy Neighbors • Routers multicasts OSPF Hello packets on all OSPF- enabled interfaces. • If two routers share a link, they can become neighbors, and establish an adjacency OSPF HELLO 10.10.10.1 10.10.10.2 Scenario: OSPF HELLO: I heard 10.10.10.2 Router 10.1.10.2 restarts DBx • After becoming adjacent, routers exchange their link state databases thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 20

  37. Database Exchange OSPF HELLO 10.10.10.1 10.10.10.2 Scenario: OSPF HELLO: I heard 10.10.10.2 Router 10.1.10.2 restarts DBx thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 21

  38. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 OSPF HELLO: I heard 10.10.10.2 DBx thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  39. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 Discovery of OSPF HELLO: I heard 10.10.10.2 adjacency DBx After neighbors are discovered the nodes exchange their databases thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  40. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 Discovery of OSPF HELLO: I heard 10.10.10.2 adjacency DBx After neighbors are discovered the nodes exchange their databases Database Description: Sequence = X Send empty Database Description thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  41. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 Discovery of OSPF HELLO: I heard 10.10.10.2 adjacency DBx After neighbors are discovered the nodes exchange their databases Database Description: Sequence = X Send empty Sends database Database description. Database Description: Sequence = X, Description (description only 5 LSA Headers = { contains LSA Router-LSA, 10.10.10.1, 0x80000006 headers) Router-LSA, 10.10.10.3, 0x80000007 Router-LSA, 10.10.10.4, 0x8000003a Router-LSA, 10.10.10.5, 0x80000038 Router-LSA, 10.10.10.6, 0x80000005 } thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  42. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 Discovery of OSPF HELLO: I heard 10.10.10.2 adjacency DBx After neighbors are discovered the nodes exchange their databases Database Description: Sequence = X Send empty Sends database Database description. Database Description: Sequence = X, Description (description only 5 LSA Headers = { contains LSA Router-LSA, 10.10.10.1, 0x80000006 headers) Router-LSA, 10.10.10.3, 0x80000007 Router-LSA, 10.10.10.4, 0x8000003a Router-LSA, 10.10.10.5, 0x80000038 Router-LSA, 10.10.10.6, 0x80000005 Database } Description of 10.10.10.2 Database Description: Sequence = X+1 1 LSA Headers = { Router-LSA, 10.10.10.2, 0x80000005 } thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  43. Scenario: Database Exchange Router 10.10.10.2 restarts OSPF HELLO 10.10.10.1 10.10.10.2 Discovery of OSPF HELLO: I heard 10.10.10.2 adjacency DBx After neighbors are discovered the nodes exchange their databases Database Description: Sequence = X Send empty Sends database Database description. Database Description: Sequence = X, Description (description only 5 LSA Headers = { contains LSA Router-LSA, 10.10.10.1, 0x80000006 headers) Router-LSA, 10.10.10.3, 0x80000007 Router-LSA, 10.10.10.4, 0x8000003a Router-LSA, 10.10.10.5, 0x80000038 Router-LSA, 10.10.10.6, 0x80000005 Database } Description of 10.10.10.2 Acknowledges Database Description: Sequence = X+1 receipt of description 1 LSA Headers = { Router-LSA, 10.10.10.2, 0x80000005 } Database Description: Sequence = X+1 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 22

  44. Regular LSA Exchange 10.10.10.1 10.10.10.2 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 23

  45. Regular LSA Exchange 10.10.10.1 10.10.10.2 Link State Reequest packets, LSAs = { Router-LSA, 10.10.10.1, Router-LSA, 10.10.10.3, Router-LSA, 10.10.10.4, 10.10.10.2 explicitly Router-LSA, 10.10.10.5, requests each LSA Router-LSA, 10.10.10.6, from 10.10.10.1 } thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 23

  46. Regular LSA Exchange 10.10.10.1 10.10.10.2 Link State Reequest packets, LSAs = { Router-LSA, 10.10.10.1, Router-LSA, 10.10.10.3, Router-LSA, 10.10.10.4, 10.10.10.2 explicitly Router-LSA, 10.10.10.5, requests each LSA Router-LSA, 10.10.10.6, from 10.10.10.1 } 10.10.10.1 sends requested LSAs Link State Update Packet, LSAs = { Router-LSA, 10.10.10.1, 0x80000006, LSA... Router-LSA, 10.10.10.3, 0x80000007, LSA... Router-LSA, 10.10.10.4, 0x8000003a, LSA... Router-LSA, 10.10.10.5, 0x80000038, LSA... Router-LSA, 10.10.10.6, 0x80000005, LSA.... } thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 23

  47. Regular LSA Exchange 10.10.10.1 10.10.10.2 Link State Reequest packets, LSAs = { Router-LSA, 10.10.10.1, Router-LSA, 10.10.10.3, Router-LSA, 10.10.10.4, 10.10.10.2 explicitly Router-LSA, 10.10.10.5, requests each LSA Router-LSA, 10.10.10.6, from 10.10.10.1 } 10.10.10.1 sends requested LSAs Link State Update Packet, LSAs = { Router-LSA, 10.10.10.1, 0x80000006, LSA... Router-LSA, 10.10.10.3, 0x80000007, LSA... Router-LSA, 10.10.10.4, 0x8000003a, LSA... 10.10.10.2 has more Router-LSA, 10.10.10.5, 0x80000038, LSA... recent value for Router-LSA, 10.10.10.6, 0x80000005, LSA.... 10.10.1.6 and sends } it to 10.10.10.1 (with higher Link State Update Packet, sequence number) LSAs = { Router-LSA, 10.10.10.6, 0x80000006, LSA.... } thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 23

  48. Routing Data Distribution 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  49. Routing Data Distribution 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  50. Routing Data Distribution 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  51. Routing Data Distribution 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  52. Routing Data Distribution Update database 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  53. Routing Data Distribution Update database 10.10.10.1 10.10.10.2 10.10.10.4 10.10.10.6 10.10.10.3 10.10.10.5 thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 24

  54. LSA Updates • Triggered by local topology or link cost changes • A received LSA that contains no new information is suppressed • Exception: very infrequent (every 30 min) flooding • Acknowledgement: • explicit ACK • implicit via reception of LSA Update thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 25

  55. Question • What is the role of the Database Description packets? thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 26

  56. OSPF Autonomous System • A region of the Internet administered by a single entity. • Examples of autonomous regions are: • X’s campus network • Frees backbone network • Routing is done differently within an autonomous system (intradomain routing) and between autonomous system (interdomain routing). thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 27

  57. Large OSPF nets • Large link-state table • Each router maintains a LSDB for all links • The LSDB requires the use of memory • Frequent SPF calculations • Topology changes; re-run Dijkstra • Flapping links • Large routing table • Solution: Divide the network into multiple areas thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 28

  58. Multi-Area OSPF • A flapping link will affect only an area • Dijkstra only when changes within that area • Complete topology only for that area ➡ Separate large network into smaller ➡ Hierarchical routing ➡ Area == Isolation of “problems” thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 29

  59. Area 0 / Area 2 Backbone Area Area 1 Ext. AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  60. Area 0 / Area 2 Backbone Area Area 1 Internal Routers Ext. AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  61. Area 0 / Area 2 Backbone Area Area 1 Internal Routers Backbone Routers Ext. AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  62. Area 0 / Area Border Router Area 2 Backbone Area Area 1 Internal Routers Backbone Routers Ext. AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  63. Area 0 / Area Border Router Area 2 Backbone Area Area 1 Internal Routers Backbone Routers Ext. AS Border Router AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  64. Area 0 / Area Border Router Area 2 Backbone Area Area 1 Internal Routers Backbone Routers Ext. AS Border Router AS thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 30

  65. Internal Routers Backbone Routers Area Border Router AS Border Router thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 31

  66. Internal Routers Routers with all their interfaces within the same area Backbone Routers Routers with at least one interface connected to area 0 AS Border Router Routers that have at least one interface connected to an another autonomous system Area Border Router Routers with interfaces attached to multiple areas within the same autonomous system thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 32

  67. Internal Routers Backbone Routers Routers with at least one interface connected to area 0 AS Border Router Routers that have at least one interface connected to an another autonomous system Area Border Router Routers with interfaces attached to multiple areas within the same autonomous system thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 32

  68. Internal Routers Backbone Routers AS Border Router Routers that have at least one interface connected to an another autonomous system Area Border Router Routers with interfaces attached to multiple areas within the same autonomous system thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 32

  69. Internal Routers Backbone Routers AS Border Router Area Border Router Routers with interfaces attached to multiple areas within the same autonomous system thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 32

  70. Internal Routers Backbone Routers AS Border Router Area Border Router thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 32

  71. Internal Routers Backbone Routers AS Border Router Area Border Router thomas@thomasclausen.org http://www.thomasclausen.org mark@townsley.net http://www.townsley.net/ 33

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